The present invention relates to fabrication of electronic devices and circuits, and in particular to their integration into wearable textiles.
Electrical circuits are typically assembled by soldering active and passive components onto solid boards. The components receive power and exchange signals by means of a network of conductive metal traces patterned, typically, in multiple layers on the board. This approach to circuit fabrication, while virtually universal, nonetheless limits the manner in which electronic devices are housed and used. Generally, rigid boards are contained within an equally rigid cabinet, which sits on, or serves as, a piece of the user""s furniture. Indeed, the notion of electronics being packaged in xe2x80x9cboxesxe2x80x9d is so ubiquitous that alternatives are difficult to imagine.
But as the miniaturization of circuits continues, and as the range of materials from which electronic components may be formed expands, alternatives to traditional housings will assume increasing importance. In particular, much current work involving user-interface design attempts to bring electronic sensing and display circuitry into more intimate contact with users; this allows the functioning of electronic devices to become a natural part of everyday action and routine, sparing users the need to deliberately xe2x80x9coperatexe2x80x9d an external system, and rendering interaction with digital articles as natural as interaction with their traditional counterparts.
Such an approach also increase the range of useful tasks amenable to digital mediation: environmental and location monitoring, information storage, processing, and mediation, and short- or long-range digital communication all may be effected without effort by the user or proximity to an external electronic device. Thus, by associating circuitry with the user rather than requiring the user to seek out the circuitry, the user is relieved of the need to interrupt or modify ordinary behavior to interact with electronics; instead, the electronics conforms to the behavior of the user.
Integrating electronic circuitry within textiles poses difficult engineering issues if the desirable characteristics of fabric are to be combined with presently available electronic components. For example, fabrics can assume a wide variety of textures and appearances, as well as shapes and volumes; they are flexible, accommodate stress and movement without damage, and can be laundered. It is just these characteristics that traditional modalities for mounting electronic components lack. Thus, directly integrating stiffly mounted electronic circuitry into traditional textiles would defeat their fundamental appeal.
Historically, solder and solder joints have been the method of choice for providing electrical and mechanical interconnections in electrical and electronic devices. This operation (well known to those skilled in the art) is typically accomplished at temperatures of 200xc2x0 mto 300xc2x0 C. with an alloy of tin, lead, and/or silver combined with a soldering flux. The solder cools to provide not only a semipermanent electrical pathway between metallic component leads and metallic printed circuit contacts, but also the sole mechanical attachment of components to the circuit substrate. This approach has several disadvantages in the context of wearable and textile applications, chief among which are the issues of lead toxicity, the high temperatures involved (which would damage most wearable fabrics), and the rigidity of metal-to-metal solder joints which form stress concentration points when the system is flexed, folded, or sheared.
Copending application Ser. no. 08/935,466, filed on Sep. 24, 1997, discloses a variety of approaches toward integrating electrical circuitry with traditional textiles. In general, conductive fibers are integrated within the weave of the textile, serving as a substrate for the attachment of electronic components and providing connections therebetween. In particular, leads from electronic components are soldered, adhered, or fastened to the conductive fibers, which serve as electrical conduits capable of carrying data signals and/or power. In an alternative approach, the electrical conduits are strips of conductive fabric attached to a non-conductive fabric substrate.
Conventional xe2x80x9cflexxe2x80x9d circuits are typically formed by laminating alternating layers of patterned copper and polyimide. These flex circuits typically have a minimum bending radius beyond which permanent deformation or delamination will occur, so their range of motion must be constrained by the encompassing system. Furthermore, components must be placed on conventional flex circuits to avoid areas where differential flexure will stress mechanical connections between circuitry and components.
Electrical interconnects patterned in fabric substrates must be mechanically compatible with the substrate in order to retain the desirable properties of flexibility and durability that fabric provides, which properties are superior to those provided by existing flexible circuitry. Clearly it would be desirable to provide an electrical and mechanical interconnection that solves the problem of lead toxicity, does not need to be assembled at high temperatures, and provides a good xe2x80x9cmechanical impedance matchxe2x80x9d between substrate, interconnect, and components.
In accordance with the present invention, electrical circuits are created on ordinary, non-conductive fabric using electronic components with flexible leads that are conductively stitched into the fabric, and conductive traces also formed by stitching. This approach not only permits integration of electronics with conventional fabrics, but also preserves the fabric character of the final article. Moreover, the operative electronic elements of the components are preferably contained within watertight packages, allowing the fabric and circuitry affixed thereto to be laundered in any conventional manner. The packages themselves may be round or polygonal (i.e., having three or more straight sides).
The present invention can also realize the benefits of multiple-layer circuit construction. In conventional circuitry, each board layer is printed or etched in copper on one side of a thin insulating substrate, and the substrates are then laminated together; holes are drilled where layers are to interconnect, and are plated to form electrically conductive xe2x80x9cvias.xe2x80x9d In accordance with the present invention, fabric layers having conductive traces thereon are separated from each other by nonconductive sheets, and the layers are conductively stitched where the traces of different layers are to make contact.
Accordingly, in a first aspect, the invention makes use of stitchable electrical components having flexible, conductive leads and encased, at least partially, in watertight packages. To form a circuit, the leads are conductively stitched to a textile panel so as to afford insulation space between the leads, and traces are stitched between at least some of the leads so as to form an electrical circuit.
In a second aspect, a multi-level circuit is created by stitching conductive traces on a second textile panel, bringing the panels into alignment, disposing a nonconductive sheet between the panels, and establishing electrical connections between the traces of the first panel and the traces of the second panel at selected points of overlap therebetween by conductively stitching the traces together at these points.
As used herein, the term xe2x80x9cstitchingxe2x80x9d refers broadly to any form of sewing on a textile (i.e., a pre-existing matrix of woven fibers), whether for purposes of attachment to the textile or creation of a path or xe2x80x9ctracexe2x80x9d along the textile. Accordingly, stitching includes, without limitation, sewing, embroidery, couching, weaving, knitting, braiding, and needlepunching.